1. Field of the Invention
The present invention relates generally to subterranean pipe string joint locators, and more particularly, to a joint locator and methods for positioning a well tool connected to coiled tubing in a well.
2. Description of the Prior Art
In the drilling and completion of oil and gas wells, a well bore is drilled into the subterranean producing formation or formations. A string of pipe, e.g., casing, is typically then cemented in the well bore, and a string of additional pipe, known as production tubing, for conducting produced fluids out of the well bore is disposed within the cemented string of pipe. The subterranean strings of pipe are each comprised of a plurality of pipe sections which are threadedly jointed together. The pipe joints, also often referred to as collars, are of increased masses as compared to other portions of the pipe sections.
It is often necessary to precisely locate one or more of the pipe joints of the casing, a liner or the production tubing in a well. This need arises, for example, when it is necessary to precisely locate a well tool such as a packer within one of the pipe strings in the well bore. The well tool is typically lowered into the pipe string on a length of coiled tubing, and the depth of a particular pipe joint adjacent or near the location to which the tool is to be positioned can be readily found on a previously recorded joint and tally log for the well. That is, after open hole logs have been run in a drilled well bore and one or more pipe strings have been cemented therein, an additional log is typically run within the pipe strings. The logging tools used include a pipe joint locator whereby the depths of each of the pipe joints through which the logging tools are passed is recorded. The logging tools generally also include a gamma ray logging device which records the depths and the levels of naturally occurring gamma rays that are emitted from various well formations. The additional log is correlated with the previous open hole logs which results in a very accurate record of the depths of the pipe joints across the subterranean zones of interest referred to as the joint and tally log. Given this readily available pipe joint depth information, it would seem to be a straightforward task to simply lower the well tool connected to a length of coiled tubing into the pipe string while measuring the length of coiled tubing in the pipe string by means of a conventional surface coiled tubing measuring device until the measuring device reading equals the depth of the desired well tool location as indicated on the joint and tally log. However, no matter how accurate the coiled tubing surface measuring device is, the true depth measurement is flawed due to effects such as coiled tubing stretch, elongation from thermal effects, sinusoidal and helical buckling, and a variety of other often unpredictable deformations in the length of coiled tubing suspended in the well bore.
Heretofore, attempts have been made to more accurately control the depth of well tools connected to coiled tubing. For example, a production tubing end locator has been utilized attached at the end of the coiled tubing. The production tubing end locator tool usually consists of collets or heavy bow springs that spring outwardly when the tool is lowered beyond the end of the production tubing string. When the coiled tubing is raised and the tool is pulled back into the production tubing string, a drag force is generated by the collets or bow springs that is registered by a weight indicator at the surface.
The use of such production tubing string end locator tools involve a number of problems. The most common problem is that not all wells include production tubing strings and only have casing or are produced open hole. Thus, in those wells there is no production pipe string for the tool to catch on while moving upwardly. Another problem associated with using the lower end of the production tubing string as a location point is that the tubing end may not be accurately located with respect to the producing zone. Tubing section lengths are tallied as they are run in the well and mathematical or length measurement errors are common. Even when the tubing sections are measured and tallied accurately, the joint and tally log can be inaccurate with respect to where the end of the tubing string is relative to the zone of interest. Yet another problem in the use of production tubing end locator tools is that a different size tool must be used for different sizes of tubing. Further, in deviated or deep wells, the small weight increase as a result of the drag produced by the end locator tool is not enough to be noticeable at the surface.
While a variety of other types of pipe string joint indicators have been developed including slick line indicators that produce a drag inside the tubing string, wire line indicators that send an electronic signal to the surface by way of electric cable and others, they either can not be utilized as a component in a coiled tubing-well tool system or have disadvantages when so used.
Thus, there is a need for an improved coiled tubing joint locator tool and methods of using the tool whereby the locations of pipe string joints can accurately be determined as the coiled tubing is lowered in a well and while fluid is flowed through the coiled tubing into a pipe string in which it is located.